Thermal properties of ternary Ge–Sb–Se chalcogenide glass for use in molded lens applications

• Compositional dependence of thermal properties of Ge–Sb–Se glasses for molded IR lens applications is investigated.
• Ge turns out to be most influential in glass transition and softening point temperatures.
• Thermal properties are closely connected with mean coordination number and average bond energy.

As for the molded lens applications of ternary Ge–Sb–Se glass, Ge-rich compositions are normally preferable since thermal and mechanical properties are better in these compositions. In an effort to explicate thermal properties of such glasses suitable for practical molding process, we have evaluated their compositional dependence of glass transition temperature (Tg) and softening point temperature (Ts). Among three constituent atoms, Ge turns out to exert a most conspicuous correlation with Tg and Ts. This phenomenological behavior is then explained in connection with structural evolution induced by Ge. Based on analysis of mean coordination number and average bond energy, it is inferred that the glass structure becomes energetically more stable and topologically more connected with increasing Ge content.